A method for decoding a digital signal is already known where the digital signal is-a pulse-width modulated signal. The signal can assume two states: a high signal level and a low signal level. In pulse-width modulation, a certain time (total pulse width) is provided for each bit to be transferred. The signal first assumes the low level and then the high level during the total pulse width, with the duration of the high signal level constituting either one-third or two-thirds of the total pulse width. Other proportions are, of course, also conceivable. The first case corresponds to a coded binary zero, the second case corresponds to a binary one. This bit is decoded by measuring the signal level at a point approximately mid-way through the total pulse width. For this purpose, the decoder is provided with an oscillator to reliably measure the middle of the total pulse width.
Including an oscillator increases the cost of the decoder. If longer bit streams are to be decoded, the oscillator must have high accuracy and the total pulse widths of the individual bits must be reproducible to a high degree. This requirement makes the use of high-precision and accurately adjusted oscillators necessary both in the encoder and the decoder.
Furthermore, unpublished German Patent Application No. 196 162 93.9 discloses a bus system for transmitting messages between a controller and a peripheral unit, wherein the controller sends messages of high and low urgency to the peripheral unit. The high-urgency messages have a greater amplitude and data transmission rate than the low-urgency messages. The messages consist of digital signals, where a binary zero corresponds to a low signal level, and a binary one corresponds to a high signal level.